LED display module

ABSTRACT

An LED display module is disclosed. The LED display module includes: a micro-LED array including a plurality of pixel units arrayed in a matrix with rows and columns, each of the pixel units including a red LED, a green LED, and a blue LED; a substrate including a top layer on which the pixel units are mounted, a first layer located under the top layer, and a second layer located under the first layer; and pairs of electrode pads disposed on the substrate and to which first electrodes and second electrodes of the LEDs of the pixel units are connected. The distances between peripheral portions of the paired electrode pads are longer than the distances between central portions thereof.

This is a continuation of U.S. patent application Ser. No. 16/242,203,filed Jan. 8, 2019, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an LED display module, and morespecifically to an LED display module for a full-color LED displaydevice including pixel units, each of which includes LEDs emitting lightof different wavelengths, wherein the distances between electrodepatterns formed on a substrate can be more efficiently secured, thenumber of layers constituting the substrate can be reduced, and routingcan be more simply implemented.

2. Description of the Related Art

Display devices using light emitting diodes (LEDs) as backlight sourceshave been proposed. Particularly, full-color LED display devices havebeen proposed in which LEDs emitting light of different wavelengths aregrouped into pixels and the pixels are arrayed in a matrix. Each of thepixels consists of red, green, and blue LEDs or red, green, blue, andwhite LEDs. In a package type full-color LED display device, packagesstructures, each of which includes a red LED, a green LED, and a blueLED, are mounted on a substrate. However, the intervals between theconstituent LEDs of each pixel are above a predetermined level, makingit difficult to obtain high-quality resolution.

Single-pixel LED packages have been proposed in which red, green, andblue LED chips are mounted to constitute one pixel. Multi-pixel LEDpackages have also been proposed in which several pixels are mounted inone package. Such single-pixel LED packages or multi-pixel LED packagesrequire a large number of terminals to individually drive red, green,and blue LEDs. The large number of terminals involves many limitationsin implementing routing, increases the possibility of shorting betweeninterconnection lines, and causes limitations in designing circuits onPCBs mounted with LED packages.

The formation of electrode patterns on a substrate in the constructionof a conventional LED display module significantly limits the yield ofthe LED display module. Several thousands to millions of pixels arerequired per unit module and a plurality of electrode pads should beformed corresponding to the number of LEDs in one pixel. That is, thereare many limiting factors associated with the sizes and intervals of theplurality of electrode pads.

FIGS. 1 to 3 illustrate problems caused by electrode pads in theconstruction of a conventional LED display module. Specifically, FIG. 1illustrates one pixel unit in an LED display module used for thefabrication of a conventional LED display device, FIG. 2 is a verticalcross-sectional view taken along line I-I of FIG. 1, and FIG. 3illustrates layers L1, L2, and L3 in the vertical cross-sectional viewof FIG. 2 when extended to the LED display module including arrays of aplurality of pixel units.

Referring to FIGS. 1 to 3, a red LED PL1, a green LED PL2, and a blueLED PL3 are mounted on corresponding electrode pads in one pixel unit.The electrode pads mounted with the red LED PL1 are designated byreference numerals R1 a and R1 b, the electrode pads mounted with thegreen LED PL2 are designated by reference numerals G1 a and G1 b, andthe electrode pads mounted with the blue LED PL3 are designated byreference numerals B1 a and B1 b. As illustrated, each of the electrodepads has a substantially rectangular shape in cross section.

FIG. 2 is a cross-sectional view of the pixel unit, specifically avertical cross-section taken along line I-I of FIG. 1. A substrate has amultilayer structure consisting of a top layer TOP, a first layer L1, asecond layer L2, and a third layer L3 formed in this order from the topto the bottom. For matrix array and interconnection, vias RV1, GV1, andBV1 are formed to connect the left electrode pads R1 a, G1 a, and B1 aformed on the top layer TOP to interconnection lines. The left electrodepads R1 a, G1 a, and B1 a are interconnected such that an electriccurrent is allowed to flow into a drive IC (not illustrated) toindividually control the LEDs. To this end, cathode terminals of theLEDs are connected to the left electrode pads. Specifically, the cathodeterminals of the red LED PL1, the green LED PL2, and the blue LED PL3 inthe pixel unit are connected to R1 a, G1 a, and B1 a, respectively, suchthat the LEDs are individually controlled by the pixel driving IC (notillustrated).

The right electrode pads R1 b, G1 b, and B1 b corresponding to the LEDsPL1, PL2, and PL3 in the pixel unit are connected to interconnectionlines through which scan signals are received. Anode terminals of theLEDs PL1, PL2, and PL3 in the pixel unit are connected to the rightelectrode pads R1 b, G1 b, and B1 b, respectively.

The first layer L1 is located under the top layer TOP. A B contact BC1is formed at a position of the first layer L1 corresponding to the Belectrode pad B1 a disposed on the top layer TOP. Referring to FIG. 3illustrating an array structure of the plurality of pixel units, Bcontacts BC1, BC2, and BC3 are formed at positions corresponding to theB electrode pads and a B interconnection line 11 is formed to connectthe B contacts BC1, BC2, and BC3 to one another. The B contacts BC1,BC2, and BC3 are connected to the corresponding B electrode pads B1, B2,and B3 through B vias BV1. The second layer L2 is located under thefirst layer L1. G contacts GC1, GC2, and GC3 are formed at positions ofthe second layer L2 corresponding to the G electrode pads G1, G2, and G3disposed on the top layer and a G interconnection line 12 is formed toconnect the G contacts GC1, GC2, and GC3 to one another. The G contactsGC1, GC2, and GC3 are connected to the corresponding G electrode padsG1, G2, and G3 through G vias GV1. The third layer L3 is located underthe second layer L2. R contacts RC1, RC2, and RC3 are formed atpositions of the third layer L3 corresponding to the R electrode padsR1, R2, and R3 disposed on the top layer and an R interconnection line13 is formed to connect the R contacts RC1, RC2, and RC3 to one another.The R contacts RC1, RC2, and RC3 are connected to the corresponding Relectrode pads R1, R2, and R3 through R vias RV1. The electrode pads R1b, G1 b, and B1 b connected with the anode terminals in the pixel unitsare disposed such that scan signals are received in rows throughrow-wise interconnections (not illustrated) formed in one of the firstto third layers.

In the construction of the conventional LED display module, the LEDsPL1, PL2, and PL3 (specifically, the electrodes of the LEDs) of thepixel units are electrically connected to and mounted on the electrodepads R1 a, R1 b, G1 a, G1 b, B1 a, and B1 b by a reflow process usingsolder balls (SB1, SB2, and SB3 in FIG. 2).

However, the solder balls melted during the reflow process tend to flowinto edge areas (E of FIG. 1) of the electrode pads formed on thesubstrate due to the rectangular shape of the electrode pads, and as aresult, the LEDs mounted on the electrode pads are tilted. This tiltingleads to the formation of defects and low yield of the LED displaymodule.

A multilayer substrate may be used for efficient interconnection. Inthis case, interconnection between the layers of the substrate throughvias should also be taken into consideration. That is, considering therelationship between electrode pads and corresponding vias connectedthereto, the outer circumferences of the cross sections of the verticalvias should be within the outer circumferences of the electrode padssuch that the underlying vias are not misaligned with the overlyingelectrode pads. However, a reduction in the cross-sectional area of theelectrode pads is insufficient to solve the problem that the LEDs aretilted during reflow.

Furthermore, the increased number of the layers in the multilayersubstrate and the small intervals between interconnection lines withinthe layers cause frequent shorting and make the implementation ofrouting excessively complex.

Thus, there is a need in the art to provide a solution to the multipleproblems of the prior art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to effectively solvethe problems encountered in conventional LED display modules, and it isan object of the present invention to provide an LED display module inwhich solder balls melted during a reflow process do not flow into edgeareas of electrode pads, whose cross-sectional shape is rectangular inconventional LED display modules, to prevent LEDs mounted on theelectrode pads from being tilted and the electrode pads can beeffectively connected to corresponding vias in a multilayer substrate.

An LED display module according to one aspect of the present inventionincludes: a micro-LED array including a plurality of pixel units arrayedin a matrix with rows and columns, each of the pixel units including ared LED, a green LED, and a blue LED; a substrate including a top layeron which the pixel units are mounted, a first layer located under thetop layer, and a second layer located under the first layer; and pairsof electrode pads disposed on the substrate and to which firstelectrodes and second electrodes of the LEDs of the pixel units areconnected, wherein the distances between peripheral portions of thepaired electrode pads are longer than the distances between centralportions thereof.

According to one embodiment, the pairs of electrode pads include aplurality of first electrode pads to which the first electrodes of theLEDs of the pixel units are connected and a plurality of secondelectrode pads to which the second electrodes of the LEDs of the pixelunits are connected.

According to one embodiment, the plurality of first electrode padscorresponding to each pixel unit include a first R electrode pad, afirst G electrode pad, and a first B electrode pad; and the plurality ofsecond electrode pads corresponding to each pixel unit include a secondR electrode pad, a second G electrode pad, and a second B electrode pad.

According to one embodiment, the first electrode pads corresponding toone pixel unit and the first electrode pads corresponding to anotherpixel unit adjacent in the row direction receive scan signals appliedthrough a common row-wise interconnection line; and the second electrodepads corresponding to one pixel unit are connected to the secondelectrode pads corresponding to another pixel unit adjacent in thecolumn direction through a common column-wise interconnection line.

According to one embodiment, the pairs of electrode pads are disposed onthe top layer.

According to one embodiment, the column-wise interconnection lines areformed on the second layer.

According to one embodiment, the column-wise interconnection lines areconnected to the first electrode pads through first vias.

According to one embodiment, the row-wise interconnection lines areformed on the first layer.

According to one embodiment, the row-wise interconnection lines areconnected to the second electrode pads through second vias.

According to one embodiment, the second R electrode pads adjacent in thecolumn direction are linearly aligned, the second G electrode padsadjacent in the column direction are linearly aligned, and the second Belectrode pads adjacent in the column direction are linearly aligned.

According to one embodiment, each of the column-wise interconnectionlines includes three sub-lines consisting of an R line, a G line, and aB line.

According to one embodiment, the second R electrode pads adjacent in thecolumn direction are connected to the R line, the second G electrodepads adjacent in the column direction are connected to the G line, andthe second B electrode pads adjacent in the column direction areconnected to the B line.

According to one embodiment, the outer circumference of the upper end ofeach of the first vias is within the outer circumference of thecorresponding first electrode pad in the connection portion between thefirst electrode pad and the first via.

According to one embodiment, each of the first electrode pads has acircular or n-gonal shape (n is a natural number of 5 or greater) incross section.

According to one embodiment, the outer circumference of the upper end ofeach of the second vias is within the outer circumference of thecorresponding second electrode pad in the connection portion between thesecond electrode pad and the second via.

According to one embodiment, each of the second electrode pads has acircular or n-gonal shape (n is a natural number of 5 or greater) incross section.

According to one embodiment, the first and second electrode padscorresponding to each pixel unit are arrayed in the row and columndirections, respectively.

According to one embodiment, the number of the row-wise interconnectionlines corresponds to the number of the rows.

According to one embodiment, scan signals are sequentially applied tothe common row-wise interconnection lines in response predetermined scancycles.

According to one embodiment, the number of the column-wiseinterconnection lines corresponds to the number of the columns.

The LED display module of the present invention is free from theproblems encountered in conventional LED display modules includingelectrode pads whose cross-sectional shape is rectangular. Specifically,the solder balls melted during a reflow process do not flow into edgeareas of the electrode pads to prevent tilting of the LEDs mounted onthe electrode pads, resulting in high yield of the LED display module.

In addition, the number of the layers in the multilayer substrate of theLED display module according to the present invention is reduced and thepossibility of shorting between the interconnection lines can bereduced. Furthermore, routing can be more simply implemented in the LEDdisplay module of the present invention than in conventional LED displaymodules.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 illustrates one pixel unit in a conventional display module;

FIG. 2 is a vertical cross-sectional view taken along line I-I of FIG.1;

FIG. 3 illustrates layers L1, L2, and L3 in the vertical cross-sectionalview of FIG. 2 when extended to the LED display module including arraysof a plurality of pixel units;

FIG. 4 illustrates one pixel unit of a display module according to oneembodiment of the present invention;

FIG. 5 is a vertical cross-sectional view taken along line II-II of FIG.4;

FIG. 6 illustrates exemplary electrode pads of the display module ofFIG. 4;

FIG. 7 illustrates a top layer TOP, a first layer L10, and a secondlayer L20 in the vertical cross-sectional view of FIG. 5 when extendedto the LED display module including arrays of a plurality of pixelunits; and

FIG. 8 illustrates (a) the top layer of FIG. 7, (b) a cross-sectionalview taken along line of (a), and (c) a cross-sectional view taken alongline IV-IV of (a).

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described withreference to the accompanying drawings. It should be noted that thedrawings and embodiments are simplified and illustrated such that thoseskilled in the art can readily understand the present invention.

FIG. 4 illustrates one pixel unit of a display module according to oneembodiment of the present invention, FIG. 5 is a verticalcross-sectional view taken along line of FIG. 4, FIG. 6 illustratesexemplary electrode pads of the display module of FIG. 4, FIG. 7illustrates a top layer TOP, a first layer L10, and a second layer L20in the vertical cross-sectional view of FIG. 5 when extended to the LEDdisplay module including arrays of a plurality of pixel units, and FIG.8 illustrates (a) the top layer of FIG. 7, (b) a cross-sectional viewtaken along line of (a), and (c) a cross-sectional view taken along lineIV-IV of (a).

An LED display module of the present invention includes: a micro-LEDarray including a plurality of pixel units arrayed in a matrix with rowsand columns, each of the pixel units including a red LED, a green LED,and a blue LED; a substrate including a top layer on which the pixelunits are mounted, a first layer located under the top layer, and asecond layer located under the first layer; and pairs of electrode padsdisposed on the substrate and to which first electrodes and secondelectrodes of the LEDs of the pixel units are connected.

Each of the pixel units includes a red LED PL11, a green LED PL12, and ablue LED PL13, as illustrated in FIG. 4. The LEDs PL11, PL12, and PL13are mounted on the corresponding pairs of electrode pads. Specifically,the red LED PL11 is mounted on the pair of R electrode pads R11 a andR11 b, the green LED PL12 is mounted on the pair of G electrode pads G11a and G11 b, and the blue LED PL13 is mounted on the pair of B electrodepads B11 a and B11 b.

The pairs of electrode pads R11 a, R11 b, G11 a, G11 b, B11 a, and B11 bare divided into first electrode pads R11 a, G11 a, and B11 a and secondelectrode pads R11 b, G11 b, and B11 b. Specifically, the pair of Relectrode pads R11 a and R11 b are divided into a first electrode padR11 a to which a first electrode of the red LED PL11 is connected and asecond electrode pad R11 b to which a second electrode of the red LEDPL11 is connected; the pair of G electrode pads G11 a and G11 b aredivided into a first electrode pad G11 a to which a first electrode ofthe green LED PL12 is connected and a second electrode pad G11 b towhich a second electrode of the green LED PL12 is connected; and thepair of B electrode pads B11 a and B11 b are divided into a firstelectrode pad B11 a to which a first electrode of the blue LED PL13 isconnected and a second electrode pad B11 b to which a second electrodeof the blue LED PL13 is connected. Considering the construction of theLED display module in which the pixel units are arrayed in a matrix withrows and columns, the plurality of pairs of electrode pads on which thepixel units are mounted should be disposed at substantially the sameintervals and have the same size in limited areas on the substrate. Thesize of the LEDs should also be taken into consideration. For thesereasons, the size of the electrode pads is significantly limited. Whenit is desired to reduce the size of the electrode pads, connectionportions between vias formed in the multilayer substrate and theelectrode pads should also be taken into consideration for efficientinterconnection. In the case where the electrode pads are increased insize or have a rectangular shape in cross section, as in conventionalelectrode pads, solder balls flow into edges (see “E” of FIG. 1) of theelectrode pads during a reflow process, as mentioned above. As a result,the LED chips mounted on the electrode pads are tilted, seriouslyaffecting the yield of the LED display module.

Thus, the LED display module of the present invention is designed suchthat when the pairs of electrode pads (for example, R11 a and R11 b) arearranged on the substrate, the distances between peripheral portions ofthe paired electrode pads are longer than the distances between centralportions thereof.

Each of the pairs of electrode pads to which the first electrodes andthe second electrodes of the LEDs of the corresponding pixel units areconnected include facing portions. The distances between the facingportions of each of the pairs of electrode pads are not constant and areshorter than the distances between central portions thereof, unlike inconventional LED display modules including electrode pads whosecross-sectional shape is quadrangular. Here, the facing portions referto portions of the paired electrode pads (for example, the firstelectrode pad R11 a and the second electrode pad R11 b) facing eachother. The facing portions are defined as the outer circumferences F1and F2 of the paired electrode pads close to each other where a line L1connecting the lowest points of the electrode pads forms an acute angleA with the tangent L2 to a point on the outer circumferences of theelectrode pads, as illustrated in FIG. 6. The angle A is measured in thecounterclockwise direction from the line connecting the lower ends ofthe electrode pads and is measured in the clockwise direction from theline connecting the upper ends of the electrode pads in the drawing. Thedistance between the central portions is defined as the distance d1between two points in the facing portions of the electrode pads on aline connecting the central portions of the electrode pads. That is, d1is the shortest distance between the electrode pads. The first electrodepad R11 a and the second electrode pad R11 b may be circular in crosssection, as illustrated in (a) of FIG. 6. In this case, when each of theelectrode pads R11 a and R11 b is divided into two by a vertical linepassing its center, the facing portions are the right half of the outercircumference of the first electrode pad R11 a and the left half of theouter circumference of the second electrode pad R11 b. When theelectrode pads are circular in cross section, as illustrated in (a) ofFIG. 6, or have corners facing each other, the distance d1 between thecentral portions is defined by only one straight line. Alternatively,the first electrode pad R11 a and the second electrode pad R11 b may bepolygonal in cross section, as illustrated in (b) of FIG. 6. In thiscase, several shortest distances d1 exist between some areas of thefacing portions of the electrode pads and are also defined as thedistances between the central portions of the electrode pads. When theelectrode pads are polygonal in cross section, as illustrated in (b) and(c) of FIG. 6, the facing portion of each of the electrode pads accountsfor less than half of the outer circumference of the electrode pad. Theperipheral portions refer to areas of the facing portions other than theportions having the shortest distance d1. The distance between theperipheral portions is relatively long compared to the distance betweenthe central portions.

A vertical cross-sectional view of the multilayer substrate taken alongline II-II of FIG. 4 is illustrated in FIG. 5. Referring to FIG. 5, thefirst electrode pads R11 a, G11 a, and B11 a are located under the LEDsPL11, PL12, and PL13 constituting one pixel unit, respectively. Here,R11 a, G11 a, and B11 a are referred to as a first R electrode pad, afirst G electrode pad, and a first B electrode pad, respectively, whichare used to distinguish the first electrode pads from one another. Thefirst electrode of the red LED PL11 is connected to the first Relectrode pad R11 a, the first electrode of the green LED PL12 isconnected to the first G electrode pad G11 a, and the first electrode ofthe blue LED PL13 is connected to the first B electrode pad B11 a.Although not illustrated, the same also applies to the connectionstructures between the second electrodes of the LEDs and the secondelectrode pads. However, connections between vias and interconnectionlines formed under the electrode pads are different from the above,which will be explained with reference to (c) of FIG. 8. The firstelectrode and the second electrode of each of the LEDs may be a cathodeterminal and an anode terminal, respectively.

The pairs of electrode pads are formed on the top layer TOP, row-wiseinterconnection lines (not illustrated) are formed on the first layerL10, and column-wise interconnection lines (not illustrated) are formedon the second layer L20. The LED display module includes first viasRV11, GV11, and BV11 connecting the column-wise interconnection lines tothe first electrode pads R11 a, G11 a, and B11 a, respectively, andsecond vias (see CV21 in (c) of FIG. 8) connecting the row-wiseinterconnection lines to the second electrode pads. In FIG. 5, RC11,GC11, and BC11 are contacts for connection to the column-wiseinterconnection lines and SB11, SB12, and SB13 are solder balls forelectrical connection between the first electrodes of the LEDs PL11,PL12, and PL13 and the first electrode pads R11 a, G11 a, and B11 aformed on the top layer TOP through a reflow process, respectively.Although not illustrated, the same also applies to the connectionstructures between the second electrodes of the LEDs PL11, PL12, andPL13 and the second electrode pads.

Some examples of the pairs of electrode pads are illustrated in FIG. 6.Each of the paired electrode pads illustrated in (a) of FIG. 6 has acircular shape in cross section. Alternatively, each of the pairedelectrode pads may have a truncated polygonal shape in cross section.For example, each of the paired electrode pads has a truncated squareshape in cross section, as illustrated in (b) of FIG. 6. Alternatively,each of the paired electrode pads may have a hexagonal cross-sectionalshape whose corners face each other. That is, each of the pairedelectrode pads may have a shape rather than a rectangular shape in crosssection. The paired electrode pads may have such a shape that thedistances d1 and d2 between the facing portions are not constant and thedistance d1 between the central portions is shorter than the distancebetween the peripheral portions.

In FIG. 6, the first via RV11 connects the first R electrode pad R11 ato the column-wise interconnection line formed on the second layer L2and the second via CV11 connects the second R electrode pad R11 b to therow-wise interconnection line. As mentioned previously, the outercircumferences of the upper ends of the first vias are designed not toexceed the outer circumferences of the first electrode pads even whenthe pairs of electrode pads are reduced in area. Likewise, the outercircumferences of the upper ends of the second vias are designed not toexceed the outer circumferences of the second electrode pads. The pairsof electrode pads may have various structures other than the structuresexemplified in FIG. 6. For example, the pairs of electrode pads may havea pentagonal or higher polygonal shape whose edges are curved.

Next, a structure of the LED display module in which a plurality ofpixel units are arrayed in a matrix will be explained with reference toFIGS. 7 and 8. Referring to FIGS. 7 and 8, the LED display moduleincludes a micro-LED array including pixel units arrayed in a matrixwith rows in the direction D1 and columns in the direction D2. Each ofthe pixel units includes a red LED PL11, a green LED PL12, and a blueLED PL13 (see FIG. 4). Herein, the row direction D1 refers to thedirection along which scan signals are applied in common when scanned inrows and the column direction D2 refers to the direction for currentsinking. The pixel units are connected to one another in the rowdirection D1 and the LEDs in the pixel units are connected to oneanother in the column direction D2. Herein, it will be understood thatwhen an element is referred to as being “connected” to another element,the two elements can be directly or electrically connected to eachother. The red LED, the green LED, and the blue LED constituting each ofthe pixels in the LED display module of the present invention arepreferably flip-bonded.

The plurality of LEDs of the pixel units are mounted on a substrate inthe row direction D1 and the column direction D2. The substrate includesa top layer TOP, a first layer L10 formed under the top layer TOP, and asecond layer L20 formed under the first layer L10, which are illustratedin (a), (b), and (c) of FIG. 7, respectively. As illustrated in FIG. 8,the substrate may further include another layer under the second layerL20 for additional interconnection.

In a final full-color LED display device, the pixel units are connectedin common in rows to receive scan signals in rows in response topredetermined scan cycles in the row direction D1 and are connected to adriver IC (not illustrated) for current sinking in the column directionD2. The pixel units are connected independently in the column directionD2 such that the LEDs in each pixel unit are controllable individually.It is to be understood that first electrode pads (for example, N11, N21,and N31) mounted with first terminals of the adjacent LEDs are alsointerconnected in common in the row direction D2. Thus, the full-colorLED display device is constructed such that scan signals are received inrows in response to predetermined scan cycles from the top to the bottomor vice versa and the red LEDs, the green LEDs, and the blue LEDs in thepixel units are independently connected in the column direction D2 forcurrent sinking, enabling control over color or brightness.

A detailed discussion of the individual layers will be given below. Asillustrated in (a) of FIG. 7, a plurality of second electrode pads C11,C21, C31, . . . and a plurality of second electrode pads N11, N21, N31,. . . are formed on the top layer TOP of the substrate. In each pixelunit, the pairs of electrode pads (for example, C11 and N11) correspondto the red LED, the green LED, and the blue LED, which are mounted inthe column direction. As illustrated, the first electrode pads N11consist of a first R electrode pad R11 a, a first G electrode pad G11 a,and a first B electrode pad B11 a. The second electrode pads C11 consistof a second R electrode pad R11 b, a second G electrode pad G11 b, and asecond B electrode pad B11 b. In each pixel, the first electrodes of theLEDs are connected to the first R electrode pad R11 a, the first Gelectrode pad G11 a, and the first B electrode pad B11 a and the secondelectrodes of the LEDs are connected to the second R electrode pad R11b, the second G electrode pad G11 b, and the second B electrode pad B11b. Here, the first electrodes may be cathode terminals and the secondelectrodes may be anode terminals.

The second electrode pads R11 b, G11 b, and B11 b mounted with the LEDsconstituting one pixel unit and the second electrode pads (for example,C11 and C12) connected with the pixel units adjacent in the rowdirection D1 receive common scan signals through row-wiseinterconnection lines (30 in (b)). As illustrated, the first electrodepads R11 a, G11 a, and B11 a mounted with the LEDs constituting onepixel unit and the second electrode pads R11 b, G11 b, and B11 b arearrayed in the row direction D1. The second electrode pads (for example,N11 and N21) adjacent in the column direction D2 are connected to eachother through common column-wise interconnection lines (31R, 31G, and31B in (c)).

Thus, the pairs of first electrode pads and second electrode pads arearrayed in the row direction such that the red LED, the green LED, andthe blue LED are arrayed in the row direction D1 in one pixel unit. Whenthe number of pixel units is represented by m*n (where m is the numberof columns and n is the number of rows), the number of row-wiseinterconnection lines (reference numerals 30 a, 30 b, and 30 c in (b) ofFIG. 7) is n and the number of column-wise interconnection lines(reference numerals 31R, 31G, 31B, . . . in (c) of FIG. 7) is 3m.

In order to make the row-wise interconnection lines 30 in the firstlayer L10 located under the top layer TOP and the column-wiseinterconnection lines 31R, 31G, and 31B in the second layer L20 locatedunder the first layer L10 compact, it is preferred that the secondelectrode pads (for example, C11 and C12) adjacent in the row directionD1 are linearly aligned, the R electrode pads (for example, R11 a andR21 a) of the first electrode pads adjacent in the column direction D2are linearly aligned in the column direction D2, the G electrode pads(for example, G11 a and G21 a) of the first electrode pads adjacent inthe column direction D2 are linearly aligned in the column direction D2,and the B electrode pads (for example, B11 a and B21 a) of the firstelectrode pads adjacent in the column direction D2 are linearly alignedin the column direction D2 in the column direction D2.

The number of the row-wise interconnection lines 30 formed in the firstlayer L10 illustrated in (b) of FIG. 7 corresponds to the number of therows. Scan signals are applied in rows in response to predetermined scancycles through the row-wise interconnection lines 30, and as a result,an operating voltage is supplied to each pixel. The row-wiseinterconnection lines 30 of the first layer L10 are connected to thesecond electrode pads of the overlying top layer TOP in rows. The secondelectrode pads (for example, C21) formed on the top layer TOP areconnected to the row-wise interconnection lines (for example, 30 b)formed on the first layer L10 through vias CV21 (see the cross-section(c) of FIG. 8). Only one second via CV21 is illustrated in FIG. 8 but aplurality of vias CV21 are provided corresponding to the positions ofthe second electrode pads because the group of second electrode pads(for example, R11 b, G11 b, and B11 b) and the groups of secondelectrode pads connected to the other pixel units should be connected tothe row-wise interconnection lines of the first layer L10.

The first layer L10 may have via holes VH through which vias (RV11,GV11, and BV11 in (b) of FIG. 8) penetrate to connect the column-wiseinterconnection lines (for example, 31R, 31G, and 31B) formed on theunderlying second layer L20 to the second electrode pads N11, N21, andN31 formed on the overlying top layer TOP.

The second layer L20 is illustrated in (c) of FIG. 7. The column-wiseinterconnection lines 31R, 31G, 31B, 32R, 32G, 32B, . . . are formed onthe second layer L20. The number of the column-wise interconnectionlines may correspond to the number of the columns (m) of the pixelunits. The number of the column-wise interconnection lines is not in aone-to-one relationship with the number of the columns of the pixels. In(c) of FIG. 7, 3m interconnection lines are formed such that the LEDs ineach pixel can be controlled independently. For example, the mcolumn-wise interconnection lines designated by reference numerals 31R,31G and 31B are provided in one set. The column-wise interconnectionline 31R is an R line, the column-wise interconnection line 31G is a Gline, and the column-wise interconnection line 31B is B line. Forexample, the R electrode pads R11 a, R21 a, and R31 a adjacent in thecolumn direction are connected to the R line 31R, the G electrode padsG11 a, G21 a, and G31 a adjacent in the column direction are connectedto the G line 31G, and the B electrode pads B11 a, B21 a, and B31 aadjacent in the column direction are connected to the B line 31B.

For example, contacts (for example, RC11) with relatively wideinterconnection widths may be formed in the column-wise interconnectionlines (for example, 31R) for improved electrical connection with thefirst electrode pads (for example, R11 a) disposed on the top layer TOPthrough vias (RV11 in (b) of FIG. 8).

Referring next to FIG. 8, a further explanation will be given of theinterconnections among the top layer TOP, the first layer L10, and thesecond layer L20.

(b) of FIG. 8 is a cross-sectional view taken along line of (a) andexplains vertical structures of the first electrode pads R11 a, G11 a,and B11 a. (c) of FIG. 8 is a cross-sectional view taken along lineIV-IV of (a) and explains vertical structures of the second electrodepad C21 and the first electrode pad B21 a.

As illustrated in the cross-section ((b) of FIG. 8), the first electrodepads R11 a, G11 a, and B11 a are connected to the corresponding contactsRC11, GC11, and BC11 in the column-wise interconnections 31R, 31G, and31B (FIG. 7) formed on the second layer L20. The contacts RC11, GC11,and BC11 are connected to the first electrode pads R11 a, G11 a, and B11a through first vias RV11, GV11, and BV11 penetrating the via holes VH(FIG. 7) formed in the first layer L10. That is, each pixel unit isformed in such a manner that the R electrode pad R11 a connected withthe red LED is connected to the contact RC11 in the column-wiseinterconnection line 31R formed on the second layer L20 through thefirst via RV11, the G electrode pad G11 a connected with the green LEDis connected to the contact GC11 in the column-wise interconnection line31G formed on the second layer L20 through the first via GV11, and the Belectrode pad B11 a connected with the blue LED is connected to thecontact BC11 in the column-wise interconnection line 31B formed on thesecond layer L20 through the first via BV11.

As illustrated in the IV-IV cross-section ((c) of FIG. 8), the firstelectrode pad B21 a is connected to the contact BC21 in the column-wiseinterconnection line 31B formed on the second layer L20, whereas thesecond electrode pad B21 b is connected to the row-wise interconnectionline 30 b formed on the first layer L10 through the second via CV21.Although only the cross-section of one B21 b of the second electrodepads C21 is illustrated in (c) of FIG. 8, the same connections can applyto all second electrode pads. Thus, all second electrode pads areconnected to the row-wise interconnection lines formed on the firstlayer L10 through the first vias. As mentioned earlier, scan signals areapplied in rows through the row-wise interconnection lines (30 a, 30 b,and 30 c in FIG. 7) formed on the first layer L10.

In these figures, the numbers of the first electrode pads and the secondelectrode pads disposed on the top layer TOP, the number of the row-wiseinterconnection lines formed on the first layer L10, and the number ofthe column-wise interconnection lines formed on the second layer are mayvary (m*n) depending on the size of the LED display device.

Under an assumption that four (2*2) pixel units are arranged in the LEDdisplay module, an explanation will be given with reference to FIGS. 7and 8.

The pixel units are divided into first, second, third, and fourth pixelunits. The first pixel unit is adjacent to the second pixel unit in therow direction D1, the third pixel unit is adjacent to the fourth pixelunit in the row direction D1, the first pixel unit is adjacent to thethird pixel unit in the column direction D2, and the second pixel unitis adjacent to the fourth pixel unit in the column direction D2.

On a top layer TOP mounted with constituent LEDs of the first to fourthpixel units, a first electrode pad N11 is formed corresponding to thefirst pixel unit, a first electrode pad N12 is formed corresponding tothe second pixel unit, a first electrode pad N21 is formed correspondingto the third pixel unit, and a first electrode pad N22 is formedcorresponding to the fourth pixel unit. A second electrode pad C11corresponding to the first pixel unit, a second electrode pad C12corresponding to the second pixel unit, a second electrode pad C21corresponding to the third pixel unit, and a second electrode pad C22corresponding to the fourth pixel unit are formed on the top layer TOP.Each of the first electrode pads N11, N12, N21, and N22 includes a firstR electrode pad, a first G electrode pad, and a first B electrode pad. Afirst electrode of a red LED is connected to each R electrode pad, afirst electrode of a green LED is connected to each G electrode pad, anda first electrode of a blue LED is connected to each B electrode pad.Second electrodes of the red LED, the green LED, and the blue LED ineach pixel are connected to the corresponding second electrode pads. Thesecond electrodes are connected in common to the column-wiseinterconnection lines formed on the underlying second layer via thesecond vias. Thus, the red LED, the green LED, and the blue LED arearranged in the column direction D2 and are arrayed adjacent to oneanother in the row direction D1 in each pixel unit.

The row-wise interconnection lines 30 a and 30 b are formed on the firstlayer L10 to electrically connect the second electrode pads adjacent inthe row direction D1. The via holes VH penetrate the first layer L10 toconnect the first electrode pads to column-wise interconnection lines31R, 31G, 31B, 32R, 32G, and 32B formed on the second layer L20. Thesecond electrode pads are connected to the row-wise interconnectionlines through the second vias (CV21 in (c) of FIG. 8).

The column-wise interconnection lines 31R, 31G, 31B, 32R, 32G, and 32Bare formed on the second layer L20. In the column-wise interconnectionlines, contacts RC11, RC21, GC11, GC21, RC11, GC21, RC12, GC12, BC12,RC22, GC22, and BC22 are formed at positions corresponding to the firstelectrode pads formed on the top layer TOP. The contacts have largerwidths than the other portions of the column-wise interconnection lines.The contacts are connected to the first electrode pads through thesecond vias (RV11, GV11, and BV11 in (b) of FIG. 8).

As is apparent from the above description, the first electrodes of theLEDs are connected independently to the first electrode pads arrayed inthe row direction in each pixel of the LED display module according tothe present invention. Due to this construction, compact routing can beimplemented and pixel intervals can be reduced.

In addition, the LED display module of the present invention is freefrom the problems encountered in conventional LED display modulesincluding electrode pads whose cross-sectional shape is rectangular.Specifically, the solder balls melted during a reflow process do notflow into the edge areas of the electrode pads to prevent tilting of theLEDs mounted on the electrode pads, achieving improved yield of the LEDdisplay module.

What is claimed is:
 1. An LED display module comprising: a plurality of pixel units arrayed in a matrix with rows and columns, each of the pixel units comprising a red LED, a green LED, and a blue LED; a substrate comprising a top layer on which the pixel units are mounted, a first layer located under the top layer, and a second layer located under the first layer; and pairs of electrode pads disposed on the substrate and comprising a plurality of first electrode pads to which first electrodes of the LEDs of the pixel units are connected and a plurality of second electrode pads to which second electrodes of the LEDs of the pixel units are connected, wherein the red LED, the green LED, and the blue LED are arranged in the column direction and arrayed adjacent to the row direction in each of the pixel units.
 2. The LED display module according to claim 1, wherein the distance between peripheral portions of the paired electrode pads are longer than the distances between central portions thereof.
 3. The LED display module according to claim 1, wherein the pixel units are connected to one another in the row direction and a red LED, a green LED, and a blue LED in the pixel units are connected to one another in the column direction.
 4. The LED display module according to claim 1, wherein the first electrode pads and the second electrode pads constituting one pixel unit are arrayed in the row direction.
 5. The LED display module according to claim 1, wherein the first electrode pads of the red LEDs adjacent in the column direction are aligned in the column direction, the first electrode pads of the green LEDs adjacent in the column direction are aligned in the column direction, and the first electrode pads of the blue LEDs adjacent in the column direction are aligned in the column direction.
 6. An LED display module comprising: a plurality of pixel units arrayed in a matrix with rows and columns, each of the pixel units comprising a red LED, a green LED, and a blue LED; a substrate comprising a top layer on which the pixel units are mounted, a first layer located under the top layer, and a second layer located under the first layer; pairs of electrode pads disposed on the substrate and comprising a plurality of first electrode pads to which the first electrodes of the LEDs of the pixel units are connected and a plurality of second electrode pads to which the second electrodes of the LEDs of the pixel units are connected; and row-wise interconnection lines are formed on the first layer and column-wise interconnection lines are formed on the second layer.
 7. The LED display module according to claim 6, further comprising first vias connecting the column-wise interconnection lines to the first electrode pads and second vias connecting the row-wise interconnection lines to the second electrode pads.
 8. The LED display module according to claim 6, wherein the second electrode pads adjacent in the column direction are connected to one of the column-wise interconnection lines.
 9. The LED display module according to claim 6, wherein the number of pixel units is represented by m*n (where m is the number of columns and n is the number of rows), the number of row-wise interconnection lines is n and the number of column-wise interconnection lines is 3m.
 10. The LED display module according to claim 6, wherein the column-wise interconnection lines are formed at positions corresponding to the first electrode pads comprising larger widths than the other portions of the column-wise interconnection lines.
 11. The LED display module according to claim 6, wherein the distance between peripheral portions of the paired electrode pads are longer than the distances between central portions thereof.
 12. An LED display module comprising: a plurality of pixel units arrayed in a matrix with rows and columns, each of the pixel units comprising a red LED, a green LED, and a blue LED; a substrate comprising a top layer on which the pixel units are mounted, a first layer located under the top layer, and a second layer located under the first layer; and pairs of electrode pads disposed on the substrate and comprising a plurality of first electrode pads to which the first electrodes of the LEDs of the pixel units are connected and a plurality of second electrode pads to which the second electrodes of the LEDs of the pixel units are connected, wherein the substrate includes an additional layer under the second layer for additional interconnection.
 13. The LED display module according to claim 12, further comprising column-wise interconnection lines are formed on the second layer and connected to the first electrode pads through first vias.
 14. The LED display module according to claim 13, wherein the column-wise interconnection lines are formed at positions corresponding to the first electrode pads comprising larger widths than the other portions of the column-wise interconnection lines.
 15. The LED display module according to claim 12, further comprising row-wise interconnection lines are formed on the first layer and connected to the second electrode pads through second vias.
 16. The LED display module according to claim 15, wherein the second vias correspond to the positions of the second electrode pads.
 17. The LED display module according to claim 12, wherein the distance between peripheral portions of the paired electrode pads are longer than the distances between central portions thereof.
 18. The LED display module according to claim 12, wherein the pixel units are connected to one another in the row direction and a red LED, a green LED, and a blue LED in the pixel units are connected to one another in the column direction.
 19. The LED display module according to claim 12, wherein the first electrode pads and the second electrode pads constituting one pixel unit are arrayed in the row direction.
 20. The LED display module according to claim 12, wherein the first electrode pads of the red LEDs adjacent in the column direction are aligned in the column direction, the first electrode pads of the green LEDs adjacent in the column direction are aligned in the column direction, and the first electrode pads of the blue LEDs adjacent in the column direction are aligned in the column direction. 